There are factors adversely affecting the durability of a pneumatic tire having a belt layer buried in a tread part thereof. Such factors include separation of a cord and a coating rubber in both end portions, in the axial direction of the tire, of the belt layer. In particular, deterioration of the belt layer makes the separation of the cord and the coating rubber likely to occur. It has been pointed out that, in a process where air inside the tire permeates to the outside of the tire, oxygen in the air oxidizes the coating rubber of the belt layer, thus accelerating such deterioration of the belt layer.
In this respect, the following configuration for a pneumatic tire has been proposed. Specifically, a cord reinforcing layer is prepared by arranging multiple cords in the axial direction of the tire, and is buried in a buttress part of the pneumatic tire. In addition, the cord reinforcing layer includes a belt-inner-side part, an extending part, and a close part. The belt-inner-side part extends in a region below the belt layer. The extending part extends outward in the axial direction of the tire, and the close part is located close to the outer surface of the tire. With this configuration, air moving inside the tire is guided to the outside of the tire by using the cord reinforcing layer, so that a large amount of oxygen is prevented from passing through the vicinity of each end portion of the belt layer. As a result, the oxidation degradation of the coating rubber of the belt layer is suppressed (see, for example, Patent Document 1).
However, the following problem arises in the above-described pneumatic tire in which a cord reinforcing layer prepared by arranging multiple cords is buried in a buttress part thereof, and in which the end portion of the cord reinforcing layer is located close to the outer surface of the tire. Specifically, the buttress part is relatively frequently brought into contact with water at the time of running on a wet road surface. For this reason, if the end portion of the cord reinforcing layer is located close to the outer surface of the tire in the vicinity of the buttress part, water is fed to the belt layer via the cord reinforcing layer. In this event, the water accelerates deterioration of the belt cords, eventually leading to a reduction in the durability of the pneumatic tire. Moreover, the buttress part is deformed by a relatively large amount at the running of the tire. For this reason, if the end portion of the cord reinforcing layer is located close to the outer surface of the tire, damage is likely to originate at the close part, resulting in a cause of a reduction in the durability of the pneumatic tire as well. In other words, even if the oxidation degradation of the belt layer is prevented by using the cord reinforcing layer, an effect of improving the durability of the pneumatic tire cannot be sufficiently obtained.    Patent Document 1: Japanese Patent Application Kokai Publication No. 2003-80905